Generally, the plate type heat exchanger comprises a plurality of plates laminated through gaskets to form a plurality of passages defined between said plates, wherein two different fluids are passed through said passages to effect heat exchange between said fluids through the plates.
The plate 1 used in the plate type heat exchanger, as shown in FIG. 21, comprises a rectangular flat plate having a heat transmitting surface formed with a suitable uneven pattern (not shown), fluid passage holes 3 formed at the four corners, a gasket groove 4 formed in the periphery of the heat transmitting surface and in a region which surrounds the fluid passage holes 3, and a gasket 5 fitted in said gasket groove.
In this connection, in the case of a plate type heat exchanger handling organic solvents in the chemical and pharmaceutical industries, use is made of a resin-covered gasket 5, as shown in FIG. 22, which comprises an elastic core 5a of elastic material, such as synthetic rubber, whose side which comes in contact with the liquid is covered with a corrosion-resistant resin cover 5b of U-shaped cross section.
Conventionally, the mounting of said resin-covered gasket 5 on the plate 1 is effected by bonding it to the flat region of the gasket groove 4 by an adhesive agent 6, such as a synthetic rubber type adhesive agent or viscous tape.
However, if the resin-covered gasket 5 is mounted on the plate 1 by the adhesive agent 6, long-term use results in permeation of the organic solvent or the like into the bonded surface of the resin-covered gasket 5, dissolving and deteriorating the adhesive agent 6, mixing impurities into the liquid, leading to the disadvantage of lowering the quality of the treating liquid.
Further, if the sealing property lowers due to the dissolution and deterioration of the adhesive agent, the liquid seeps through the flat region of the gasket groove 4 into the core 5a which lacks resistant to corrosion, thus corroding and decomposing the core 5a, leading to another problem that the sealing property is further degraded.
Further, when the resin-covered gasket 5 is to have its cover renewed, it is necessary that in order to fully retain the sealing property, the old adhesive agent 6 adhering to the flat region of the gasket groove 4 be completely removed with the utmost care; thus, much labor is involved and the operating efficiency in maintenance is very low.